The present invention relates to a information recording device for recording video data compressed by using a high-efficiently encoding technique such as the video compression method according to MPEG (Moving Picture Experts Group) standard related to motion video. More specifically, this invention relates to data recording devices and video recording/reproducing devices, which can record video data at an optimal compression coding ratio on a recording area of a recording portion, allowing users to freely set a video data compression coding ratio in video recording operation without considering the quality of finally recorded images.
Conventional video recording devices, which can change a data compression coding ratio by using the MPEG algorithm, allow users to select any data compression coding ratio so that the recorded images may have a desirable quality and the data may be reduced to a desirable extent. However, these two parameters “desirable recorded image quality” and “desirable recording capacity” are in the trade-off relation, which are usually determined by each user by means of manually setting a desirable compression coding ratio.
Japanese Laid-Open Patent Publication No. 10-92106 discloses a video recording device capable of automatically selecting a data compression-coding ratio by determining it from the reserved program recording time. This is achieved by optimizing a compression coding ratio of coded data representing each of programs in timer recording reservation list based on a remaining storage capacity of a recording medium, a recording time and recording quality requirement preset in a timer recording reservation information, aiming at obtaining possibly higher quality of the recorded images.
Video information usually contains a large amount of information, e.g., a series of 30 still images per second and therefore must be compressed by the MPEG coding method to record on a recording medium such as a hard disc which is expensive and has a limited storage capacity.
Video compression methods such as the MPEG method, may achieve higher compression coding ratios by correspondingly decreasing the quality of reproducible images. Therefore, applications using the video compression algorithm usually allow users to select a desirable compression-coding ratio. It is therefore desirable to automate the user's manual operation of selecting the compression coding ratio in such a way that an optimal value is automatically determined and set, achieving an improved efficiency of recording the video data.
Japanese Laid-Open Patent Publication No. 10-92106 discloses a video recording device capable of automatically determining a compression-coding ratio based on a remaining capacity of a recording medium. The device can automatically change a compression coding ratio of data so that all programs reserved in advance for recording by timer may be recorded on a limited storage area of a recording medium with a least decrease in the quality of reproduced images with priority specified by a user. However, the device still requires the user to manually select a target compression coding ratio for each of programs to be recorded by timer.
The video compression coding method such as the MPEG algorithm can compress information by reducing redundancies in image data due to spatial correlation and temporal correlation and hence it may not select a high compression coding ratio for video sequences with essentially low redundancies of data, i.e., complex images and intensive motion scenes. The complex images and intensive motion scenes are generally included in a certain genre program such as a sport program, which, if encoded with a high compression coding ratio, may suffer considerable degradation of the reproduced images.
On the contrary, news programs containing a relatively small quantity of complex images and intensive motion scenes and hence may be recorded at a high compression coding ratio with small effects of the quality of reproduced images.